Download 32. Nutrient assimilation.pptx

Absorption
Ingestion
Photosynthesis
Each Fundamental Process of Life
Unity of Life
Universal physical
and chemical
principles
Diversity of Life
places design
constraints on
provides certain
opportunities for
Organismal
strategies
and/or
1. We’ll use clickers today
2. Circulation systems HW due on Friday
Unique Gas Exchange and Circulatory Systems
in Different Multicellular Lineages
1. 
2. 
3. 
Common genomic
toolkit from LUCAC
Ecological roles
provides molecular
solutions for
can evolve for
selection pressures
Nutrient Assimilation - Taking Up the Right Stuff
Different cells,
tissues, & organs
Nutrient Assimilation - Taking Up the Right Stuff
Absorption
Ingestion
Photosynthesis
No specializations for gas exchange and circulation in
unicellular organisms - passive diffusion only
Independent origins of gas exchange and/or circulatory
systems in various multicellular animal and plant lineages
Physicochemical constraints (Fick’s Law and HagenPoiseuille equation) operating on convergent structures
Deep molecular homologies underlie all nutritional strategies
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Big Steps in the Origin of Life
Nutrient assimilation - Unity of Life
Definition - the uptake of non-gaseous molecules from the
environment into the cell
Common features with gas exchange 1)  Transmembrane process dependent on surface area
2)  Passive diffusion down chemical (concentration) gradients
for a few molecules (such as water), but not true for most
nutrient molecules at most times
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Origin of information processing/replication system
Origin of metabolism for generating small organic
molecules and larger polymers
Origin of bioenergetics
Origin of lipid membranes defining the boundary of
life – the challenge of impermeable membranes
C & R 26.12
Gas exchange vs. nutrient assimilation/osmoregulation
Nutrient assimilation and osmoregulatory/excretory
systems exhibit deep molecular homologies
•  Homologous transport proteins operating in modern organisms
•  Carry out nutrient assimilation and osmoregulation/excretion
•  Evolved in pre-LUCAC organisms.
F Fig 6.8
amino acids
Gases - high permeability -> do not require transport proteins
Nutrients - low permeability -> require selective transport proteins
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Basic Mechanisms of Solute Transport - F. Fig. 6.29
How do membranes perform active transport?
ATP-dependent pump generates
an electrochemical gradient –
a gradient of concentration
(“chemical”) and charge (“electro”)
across the membrane.
Typical ions: H+, Na+, K+
(Simple)
ATP
Simple diffusion - passive movement of molecules through the lipid membrane
or a protein channel (also called a uniporter)
Facilitated diffusion - passive movement of molecules across the membrane
that is facilitated by a carrier/transporter
Active transport - ATP-dependent movement of molecules across the
membrane that is performed by a pump
Reminder: H+ electrochemical gradients can drive
ATP synthesis – F-type ATP synthases/ATPases
Electrochemical gradient
F. Fig. 6.22
Some examples: 1) Gas exchange regulation - stomates in plants
2) Nutrient assimilation - digestive tracts in animals
mycelia in fungi
roots in vascular plants
3) Osmoregulation – many organisms
4) Excretion - kidneys in vertebrates
5) Transport - sucrose transport in plants
6) Electrical signaling - excitable membranes
Reverse process - ATP hydrolysis can generate H+ or Na+
electrochemical gradients – P-type ATPases
F. Fig. 6.28
Na+/K+ pump
F. Fig. 9.24
Freeman Fig. 6.29
F. Fig. 9.25
General class of F-type ATPases, including ATP synthases
(H+ gradients
ATP) across the membranes of bacteria,
mitochondria, and plastids during photosynthesis and
respiration
P-type ATPases (or ATP-dependent cation pumps)
ATP
cation electrochemical gradient
For example, H+ pump, Na+/K+ pump, and Ca2+ pump
http://www.pump.ruhr-uni-bochum.de
operating across outer cell or ER membranes
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Reverse process - ATP hydrolysis can generate H+
electrochemical gradients – V-type ATPases
Unity of nutrient assimilation at molecular level –
active transport moves solutes against their gradients
Step 1. Ion pumps use ATP energy to generate electrochemical
gradients (i. e., voltage and concentration gradients) across cell
membranes.
electron microscopic images
V-type ATPases (or ATP-dependent H+ pumps)
ATP
H+ electrochemical gradient
•  H+ pump operating across many eukaryotic organelles (e.g.,
lysosomes, contractile vacuoles, and plant vacuoles)
http://www.pump.ruhr-uni-bochum.de
•  Similar structure and some homologous subunits
as the F-type
ATP synthase, but it runs in reverse
• 
Step 2. H+ electrochemical gradients can drive
nutrient uptake in all organisms - Fig. 37.23
C & R Fig. 8.17
Proton pump (all organisms)
Alberts et al. Fig. 11.13
Na+/K+ pump (animals only)
Alterative Step 2. Na+ electrochemical gradients
can also drive nutrient uptake in animals
Na+
Na+ +
Na
Na+
Na+
Na+ +
Na
Na+
Na+
3 Na+
Na+
Na+
2 K+
Molecules
using these
transporters
cations (+)
sugars
cations (+)
amino acids
anions (-)
Molecules
using these
transporters
cations (+)
sugars
cations (+)
amino acids
anions (-)
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Evolution of transport proteins
Active transport
1. 
2. 
3. 
4. 
ATPases are able to directly couple
ATP hydrolysis to the transport of
most molecules across biological
membranes.
Different transport proteins use H+
or Na+ electrochemical gradients as
the energy source for carrying out
the transport of most molecules.
Both are true.
Neither are true.
Summary - unity of nutrient assimilation at
the molecular level
Bacteria
Archaea Eukarya
Last common ancestor
or ancestral community
Phylogenetic tree of
H+/Na+ antiporter
Many transporters of ions and other small molecules display
considerable sequence and structural homology throughout
the 3 domains -> deep evolutionary roots near the origin of life
Some workers argue for very few ancestral transport genes a few ion and organic-molecule transporters that diversified to
give rise to over 1,000 transport genes in some eukaryotes.
Diversity of nutrient assimilation at
the organismal level
Universal features of nutrient assimilation in all organisms 1)  Transmembrane transport depends on ATP-dependent pumps
2)  These pumps establish H+ or Na+ electrochemical gradients for
carrying out nutrient uptake
3)  Selective transporters use these EC gradients to move
nutrients into the organism.
4)  Deep molecular homologies unify all nutritional (and
osmoregulatory) strategies
Important factors 1)  Phylogeny
2)  Nutritional strategy
3)  Food source
4)  Solute concentration
5)  Metabolic rate
6)  Organismal size
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Nutrient assimilation (absorption) - fungi
F Fig. 30.6
Nutrient assimilation (absorption) - fungi
Well-adapted for absorption
•  rapid growth
•  hydrolytic exoenzymes
•  high surface area
•  P-type H+ pump,
•  selective transporters
C & R Fig. 31.2d
C & R Fig. 37.14
Mycorrhizae - “fungus roots”
Ion assimilation (photosynthesis) - plants
Carnivorous fungus
Nutrient assimilation (ingestion) - amoeba
•  Pseudopodium engulfs small organisms
or food particles via phagocytosis.
•  Food vacuole fuses with lysosome
containing hydrolytic enzymes
•  Nutrients absorbed across lysosome
membrane via active transport (V-type
H+ pump, plus transporters)
F Fig. 38.9
F Fig. 36.2
Roots are specialized for
water and ion uptake
Thin root hairs develop
near growing root tip
Plants use homologous ATP-dependent H+ pumps to establish
H+ electrochemical gradient, which transporters use to move
ions into root cells.
C & R Fig. 8.19 and F Fig. 28.15
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Nutrient assimilation (ingestion) - ciliate
•  Cilia in oral groove
move bacteria and
other food to mouth
•  Food is engulfed via
phagocytosis, and
food vacuoles merge
with lysosomes
•  Food vacuoles move
toward apex and then
toward base
•  Undigested contents
of food vacuoles are
expelled at anal pore
F Fig. 28.12
Vertebrate small intestine
Some animal cells are also capable of phagocytosis
C & R Fig. 43.3
For example, human macrophages (“big eaters”) use fibril-like
pseudopodia to capture invading bacteria prior to phagocytosis
Vertebrate small intestine
Proteins and carbohydrates
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Higher [Na+], variable [glucose]
Broken down by enzymes into
amino acids and sugars
Na+/K+ ATPases establish
EC gradients
Transport proteins – e.g.,
Na+/amino acid (e.g., lysine)
or Na+/glucose cotransporters
More in Monday’s lecture
Na+ diffusion cotransports glucose
Lower [Na+] due to Na+/K+ pump;
Higher [glucose] due to
Na+/glucose cotransporter
Glu diffuses down its conc gradient
Lower [glucose]
Fig. 43.16
Fig. 43.16
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Study questions- Learning Objectives
1. Explain why nutrient assimilation in all organisms exhibits deep
molecular homologies.
2. Explain why nutrient assimilation occurs in different structures in
various multicellular lineages.
3. Describe the membrane(s) and the enzyme(s) responsible for
converting electrochemical gradients into high-energy phosphate
bonds of ATP.
4. Do the same for the reverse conversion of high-energy phosphate
bonds of ATP into electrochemical gradients.
5. Describe the different transporters which use the energy in an
electrochemical gradient to move ions or polar organic molecules
across a membrane.
6. Describe the different structural adaptations associated with
nutrient assimilation in a fungus, amoeba, ciliate, plant root, and
vertebrate small intestine.
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